Suppressed transient uniform detection sensitivity pir detector

Abstract

A passive analog equalizer is connected to the output of an infrared detector to provide increasing pyroelectric detector sensitivity with increasing target frequency in order to provide a detection sensitivity which is substantially flat over the target velocity range of interest. An interruptable modulator is connected to the equalized pyroelectric detector signal to shift its frequency upwardly in order to provide negligible drift, fast recovery from transients, and the ability to quickly shut down the modulator when a transient occurs. A transient detector is operative in response to transients in the pyroelectric detector output signal to provide a window during which the modulator is interrupted in order to prevent transient induced false alarms.

What is claimed is: 
     
       1. A uniform-detection-sensitivity passive infrared detector, comprising: infrared sensor means for providing a target detection signal having an amplitude that diminishes with increasing target velocity over a range of detectable target velocities,   said infrared sensor means including a pyroelectric detector; and   equalizer means coupled to the infrared sensor means for increasingly boosting the amplitude of the target detection signal with increasing target velocity so as to provide a target-velocity-compensated signal that is substantially flat over the range of detectable target velocities;   said equalizer means including an analog passive network having a resistor capacitor network.   
     
     
       2. A uniform-detection-sensitivity passive infrared detector, comprising: infrared sensor means for providing a target detection signal having an amplitude that diminishes with increasing target velocity over a range of detectable target velocities; and   equalizer means coupled to the infrared sensor means for increasingly boosting the amplitude of the target detection signal with increasing target velocity so as to provide a target-velocity-compensated signal that is substantially flat over the range of detectable target velocities;   said target-velocity-compensated signal having a frequency domain spectrum, and further including means for shifting said frequency domain spectrum upwardly in frequency to provide a frequency shifted target-velocity-compensated-signal.   
     
     
       3. The detector of claim 2, wherein said frequency domain spectrum shifting means includes a modulator. 
     
     
       4. The detector of claim 3, wherein said modulator includes a square wave chopper having a center frequency, and a fast recovery bandpass amplifier centered about the center frequency of the square wave chopper. 
     
     
       5. The detector of claim 2, further including means coupled to said infrared sensor means for detecting transients in said target detection signal; means responsive to said frequency shifted target-velocity-compensated signal for providing an alarm; and means coupled to the transient detecting means and to said alarm providing means for interrupting the alarm providing means for a preselected time whenever said transient detecting means detects a transient. 
     
     
       6. The detector of claim 5, wherein said preselected time is selected to be just so long as a nominal transient decay time thereby minimizing gaps in alarm surveillance. 
     
     
       7. A suppressed transient infrared detector for a protected region, comprising: means for sensing infrared radiation;   means for discriminating transients in the sensed infrared radiation;   means for providing an alarm in response to sensing infrared radiation; and   means for inhibiting the alarm providing means in response to discrimination of transients in the sensed infrared radiation for a preselected time window selected to both minimize false alarms as well as to minimize gaps in region surveillance.   
     
     
       8. The detector of claim 7, wherein the sensing means further includes means for providing a signal at a first bandwidth in response to sensing radiation, and further includes means for shifting said first bandwidth signal upwardly in frequency to a comparatively higher bandwidth, wherein said discriminating means further includes means for producing a discrimination signal in response to discriminating transients, and wherein said alarm providing means further includes means for providing an alarm signal in response to said comparatively higher bandwidth signal, said inhibiting means further includes means for interrupting said comparatively higher bandwidth signal to said alarm signal providing means in response to said discrimination signal. 
     
     
       9. The detector of claim 8, wherein said shifting means includes a square wave chopper for modulating the signal at a first bandwidth to said comparatively higher bandwidth, and a bandpass amplifier centered on said comparatively higher bandwidth signal. 
     
     
       10. The detector of claim 9, wherein the transient discriminating means includes a differentiator operative to produce a well-defined pulse in response to transients in the sensed infrared radiation. 
     
     
       11. The detector of claim 10, wherein said interrupting means includes means for providing a window in response to said well-defined pulse during the time interval of which said alarm signal providing means is interrupted.